interface A{
    double f(double x,double y);
}
class B implements A {
    public double f(double x ,double y){
        return x*y;
    }
    int g(int a,int b){
        return a+b;
    }
}
public class E {
    public static void main(String args[]){
        A a=new B();
        System.out.println(a.f(3,5));
        B b=(B)a;
        System.out.println(b.g(3,5));
    }
}
